1) Field of the Invention
This invention relates to an optical network system and more particularly to an optical network system and a transmission apparatus suitable for use with an optical communication system of an access region.
2) Description of the Related Art
In recent years, a broadband dedicated line service for which Gigabit Ethernet (registered trademark) or 10 Gigabit Ethernet for an enterprise network is used has been started. Also homes are being equipped with high-speed Internet environment such as ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Home) of a gigabit class. Further, environment is being prepared wherein various undertakers can provide various services such as content distribution, data center services and so forth.
Accordingly, the data transfer capacity is radically increasing in a network of an access region comparatively near to users who enjoy provision of such services as described above. Further, in communication in an access region, because of the great variation in data transfer demand due to alteration of service contents or alteration, increasing or decreasing of communication bases, a network is required which can be ready not only for provision of a broadband path but also for increasing or decreasing installation of such paths and flexible alternation of routes.
In a present situation, increase of the capacity and extension of the length of trunk system networks are being progressed radically and reduction of the cost for transmission lines can be achieved by a wavelength division multiplexing (WDM) transmission technique and an optical amplification technique. However, when compared with the progress of the trunk system networks, in networks for an access region, speed of development is slow in terms of expansion of the throughput and reduction of the cost required for a node for distributing transmission signals to users at each point. Increase of the signal processing capacity and cost reduction of nodes are essentially required for efficient working and construction of a network.
FIG. 19 is a block diagram showing a network 500 for an access region. The network 500 shown in FIG. 19 includes a central node 510 and nodes 511-1 to 511-n connected to the central node 510, and forms a star-shaped network which is adopted comparatively frequently in a network for an access region.
Referring to FIG. 19, the node 510 shown includes optic/electric interfaces 501-1 to 501-n for converting optical signals inputted thereto from the adjacent nodes 511-1 to 511-n into electric signals to be outputted, a crossbar switch 502 for exchanging the electric signals from the optic/electric interfaces 501-1 to 501-n, and electric/optic interfaces 503-1 to 503-n for converting the electric signals exchanged by the crossbar switch 502 into optical signals and outputting the optical signals to the corresponding adjacent nodes 511-1 to 511-n.
In the node 510 shown in FIG. 19 having such a configuration as described above, for example, an optical signal from the node 511-l is converted once into an electric signal by the optic/electric interface 501-1, and switching is performed for the electric signal by the crossbar switch 502 at an electric stage. Thereafter, the electric signal is converted back into an optical signal by the electric/optic interface 503-2 (or interface 503-3 to 503-n), and the optical signal is outputted. Consequently, in the node 510, a signal from an adjacent one (for example, node 511-1) of the nodes which form the star-shaped network can be distributed to a different node 511-2 (or node 511-3 to 511-n). The distribution is performed similarly also in other node to node communication.
In the network 500 described above, if the number of wavelengths of optical signals which can be used by the nodes 511-1 to 511-n is set, for example, to four, then the throughput can be increased in comparison with that in an alternative case wherein a number of waves smaller than four, for example one wave. In this instance, it is necessary for the optic/electric interfaces 501-1 to 501-n to individually include an optical branching section 501a, a number of O/E (Optic/Electric) sections 501b corresponding to the number of increased optical wavelengths, and also it is necessary for the electric/optic interfaces 503-1 to 503-n to individually include a number of E/O (Electric/Optic) sections 503a corresponding to the number of increased optical wavelengths and a multiplex section 503b. 
It is to be noted that, as a technique relating to the invention of the present application, a technique for performing a process in a unit of an optical path is disclosed in Japanese Patent Laid-Open No. 2001-358697 (hereinafter referred to as Patent Document 1). In Patent Document 1, a wavelength router is disclosed wherein optical wavelengths to be inputted and outputted between right ports #1 to #4 and left ports #1 to #4 are transferred such that four wavelengths λ1 to λ4 may not overlap with each other so that the same wavelengths may not overlap with each other in an optical fiber between wavelength routers and between ONUs (Optical Network Units).
Further, as a publicly known technique relating to the invention of the present invention, another technique is disclosed in Japanese Patent Laid-Open No. 2004-235741 (hereinafter referred to as Patent Document 2) or Japanese Patent Laid-Open No. 2004-15729 (hereinafter referred to as Patent Document 3).
However, in the configuration of the node 500 shown in FIG. 19, if the information processing capacity of the node apparatus is increased by a conventional photoelectric conversion method or electric switching method in order to expand the throughput of the network, then the node cost increases and the scale of the apparatus increases. Particularly, as shown in FIG. 19, if the number of wavelengths of optical signals which can be used by the nodes 511-1 to 511-n is increased from one to, for example, four in order to increase the throughput, then the number of signal channels increases and the number of exchanging ports of the crossbar switch 502 cumulatively increases. Therefore, the node cost increases and the scale of the apparatus increases.
As described above, in a network for an access region, the variation of data transfer demand is very great due to alternation of service contents or alternation, increasing or decreasing installation or the like of communication bases. Therefore, for example, in a case wherein processing of only several waves is involved, in another case wherein several waves are used upon initial introduction but the number of wavelengths to be processed is increased after the introduction or in a like case, a network is required which is capable of being ready for flexible route alteration in response to increasing or decreasing installation of paths. In the case described above with reference to FIG. 19, with the hope that may secure a broadband, the initial introduction cost is high and the apparatus cost per one wavelength is high.
Accordingly, in order to implement increase of the processing capacity of nodes, economization and downsizing, it is desired also for a network for an access region to have a network configuration wherein an electronic circuit of a large scales is replaced by optical parts such that the network can process in a unit of an optical path in an optical wavelength region and include nodes having a corresponding configuration.
However, all of node apparatus which are on the market at present and which are ready for a tree-shaped or star-shaped network configuration for an access region are of a fixed wavelength path type determined in advance. While the cost of the node apparatus is low, when it is tried to change wavelength path connections for interconnecting different points, setting variation by manual operation is required. Therefore, it is difficult to be flexibly ready for path connection change in response to a short term data transfer demand.
Also the technique disclosed in Patent Document 2 mentioned above relates to a network of the fixed wavelength path type determined in advance, and, in order to increase the number of wavelengths which can be handled in a unit node, also a wavelength router itself must be prepared separately. Therefore, it is difficult to flexibly alter the number of wavelengths to be used in a node in the network.
It is to be noted that the technique disclosed in Patent Document 3 is directed to implementation of such flexible wavelength path setting as described above in a network configuration of ring topology. However, the node configuration disclosed in Patent Document 3 cannot be applied to a node in a network system which adopts star-shaped or tree-shaped topology which is used frequently in an access region.